The present invention relates to a scattered light collector for collecting light scattered by an object to be examined.

Furthermore, the invention relates to a light focusing apparatus for focusing light on or in an object to be examined.

The invention further relates to a method for controlling the focus of a focused light source.

Furthermore the invention relates to a method for measuring the light scattered or originating from a point of an object.

In the technical field of materials science use is being made of Raman-probes 100 (figure 1) to analyze the molecular structure and other properties of materials by means of Raman- scattering. These Raman-probes comprise, in addition to a housing 110, excitation optics 136, 144, 148, 134 and collector optics 134, 148, 146, 142, 132. The excitation optics generally comprise a number of lenses 134, 136 to focus the light from an optical fiber 124 in a focus point 154. (Light is to be understood in its broadest sense. It not only comprises visible light, but also infrared light and ultraviolet light) .

The collector optics also comprises a number of lenses 134, 132 to couple the light into a second optical fiber 122 that conducts the light to a wavelength selective apparatus and finally to a light detector. The excitation optics and collector optics are arranged coaxially. In order to have the excitation light 156 and the collected light 152 conducted by separated optical fibers 122, 124, a dichroic mirror 148 is being used. Furthermore the optics comprise filters 142, 144, to filter the light.

One of the applications where Raman- scattering is being applied, is in the analysis of biological materials. Because it is technically difficult to manufacture sufficiently small optics, particularly in combination with short focusing distances, the application of Raman- scattering is mostly being limited to in vitro measurements. An object of the present invention is to provide alternative optical elements that are sufficiently small for performing for example in vivo measurements on biological material .

To that end the present invention provides a scattered light collector for collecting light scattered by or originating from an object to be examined and for guiding the collected light to a light detector, the collector comprising: a first free propagation region for receiving scattered light comprising a light collection end and an input grating line, and a plurality of waveguides for guiding the collected light from the free propagation region to the detector, the first ends of the waveguides forming the input grating line of the free propagation region.

If an object to be examined is excited with light in the focus point of a focused light beam, in addition to the always present Rayleigh-scattering, Raman- scattering occurs, wherein the scattered light has a wavelength different from that of the incident light. The change of wavelength provides information on the molecular structure and other properties of the object.

By collecting the scattered light in the free propagation region the collected light can be easily conducted to one or more light detectors by the waveguides. The advantage of this embodiment is that the scattered light collector can be completely implemented in thin film technology for example based on semiconductor or glass materials, whereby a particularly compact scattered light collector is obtained, sufficiently small to be applied in in vivo measurements on biological material, such as skin, lung tissue, stomach tissue, etcetera.

In order for the free propagation region to collect light scattered by the object, the free propagation region is preferably located close to an edge of the light collector. It should be noted that the point where the light is scattered or where the collected light originates from, is not necessarily located on a surface of the object to be examined, but might also be located some distance from the surface, i.e. in the object. In this particular situation, the object itself also forms a free propagation region in addition to the free propagation region that is comprised by the scattered light collector.

A further advantage is that the scattered light collector can be produced by means of lithographic techniques, therefore allowing the convenient and cheap mass production of it. It is additionally easy to integrate the further detector and signal processing circuitry by hybrid or even heterogeneous integration (for example in a System- in-a Package (SiP) or in a System-on-a-Chip (SoC) ) , providing a particularly compact measurement instrument. The ultra compact integrated optics structures obtained are sufficiently small for performing for example in vivo measurements on biological materials in combination with an endoscope. To that end, the scattered light collector can also be easily moved into the location where the measurement has to be performed, even if the location is inside a body of an organism. As the scattered light collector also has wavelength separating capacity, a further (possibly external) device to that extent is no longer needed.

It is necessary to use monochromatic light for excitation, for example, highly coherent light provided by a laser, but also light sources with reduced coherence can be used.

In a preferred embodiment the light used is coherent light from a laser. In a preferred embodiment the waveguides comprise single-mode waveguides. It is, however, also feasible to employ multi-mode waveguides.

In a further embodiment a scattered light collector is provided, further comprising a second free propagation region comprising an output grating line, for focusing the light from the waveguides into a focus point, wherein the second ends of the waveguides form the output grating line of the second free propagation region. By choosing the lengths of the waveguides relatively to each other in such a way that the collected scattered light forms a spherical wave front in the second free propagation region, the collected light is focused in a focus point of the second free propagation region. This process is the inverse of the process taking place in the first free propagation region.

A further embodiment further comprises a light detector waveguide (also called an output channel) for guiding the light focused in the focus point to a light detector. The scattered light focused in the focus point is coupled into this light detector waveguide, for subsequent conduction of the scattered light to an elsewhere positioned detector by the light detector wave guide. In a further embodiment the present invention provides a scattered light collector, further comprising a light detector, connected to one of the light detector waveguides. If the scattered light collector is implemented in semiconductor material, the light detector can advantageously, be implemented in an integrated manner by, for example, forming a photodiode at the end of a waveguide. Alternatively, the photodiode can be formed directly in the focus point to detect the light focused there. By forming the scattered light collector integrally with a light detector in semiconductor material a very tiny scattered light detector is obtained again, that is greatly suitable to provide measurements in toughly accessible locations, such as applicable with in vivo measurements. Furthermore, such a scattered light detector can be produced relatively cheap in a mass production process.

Alternatively, the light detector is external to the scattered light collector.

The invention also provides a scattered light collector, wherein the second free propagation region comprises at least one further focus point, and a second light detector waveguide, for guiding the focused light from the further focused point to a further light detector.

The position of the focus point in the second free propagation regions not only depends on the construction of the free propagation region and the phase relation of the grating waveguides, but also on the wavelength of the light. The wavelength of the scattered light therefore also determines where the focus point is formed in the second free propagation region. Providing a plurality of light detector waveguides for conducting the focused light from a focused point to a light detector therefore has the advantage that the scattered light collector can collect light of different wavelengths and conduct it to different light detectors. In this way an external wavelength selective device between the light collector and the light detector can be omitted. Additionally, the position of the focus point also depends on the position of the point where the scattered light was being scattered. Providing additional light detector waveguides therefore offers the option to collect light that is being scattered in distinct locations on the object to be examined, in order to be detected without the need to move the scattered light collector itself.

According to another aspect of the invention a light focusing apparatus is provided for focusing light on or in an object to be examined, the apparatus comprising: a plurality of waveguides for guiding light, a coupling member for coupling light from a light source into the first ends of the waveguides, and a first free propagation region at the second ends of the waveguides, for focusing light from the waveguides on or in the object, wherein the second ends of the waveguide form an output grating line.

The light focusing apparatus is in fact an inverted scattered light collector. Light, for example coming from a semiconductor laser, is coupled into the waveguides. Due to the mutual relation of the length of optical paths through the waveguides, the ends of the waveguides in the free-propagation region acts as a grating that causes an interference pattern. In the interference pattern the global maximum acts as the focus point of the light. Just like the scattered light collector this light focusing apparatus is suitable to be implemented as a SiP or a SoC, by means whereof a cheap and most of all compact light focusing apparatus is being obtained. In a further embodiment, the invention provides a light focusing apparatus, wherein the coupling member comprises a second free propagation region comprising an input grating line formed by the first ends of the waveguide. By placing a light source in a focus point of the second free propagation region, light from the light source is coupled into the waveguides. When the light exits the waveguides in the first free propagation region, a converging wave front is created causing the light to be focused in a focus point.

In a preferred embodiment a light focusing apparatus is provided, further comprising: a light source positioned with respect to the coupling member such that light emitted by the light source is coupled into in the waveguides by the coupling member.

In a further preferred embodiment the light focusing apparatus is implemented as a SiP or a SoC.

In again a further preferred embodiment the light focusing apparatus is implemented in semiconductor material, and the light source comprises a semiconductor laser, therewith providing an integrated focused light source that is specifically suitable for, for example, in vivo measurements due to its compactness.

A further embodiment according to the invention provides a light focusing apparatus, further comprising: wavelength control means connected to the light source, for controlling the wavelength of the light emitted by the light source. The wavelength control means enable the excitation of the object to be examined with light of different wavelengths, for example, to determine the response of the material of the object to light with different wavelengths. Furthermore, the wavelength control means provides an alternative for controlling the location of the focus point, because this location also depends on the wavelength of the light.

In a quite advantageous embodiment the invention provides a light scattering detector comprising: a scattered light collector and a light focusing apparatus. In one embodiment the scattered light collector and the light focusing apparatus each comprise separate first and second free propagation regions and waveguides while in another embodiment the first and second free propagation regions and the waveguides are shared among the scattered light collector and the light focusing apparatus. In the latter case the focus point of the excitation light in the second free propagation region is a different focus point than the focus point of the collected light in the second free propagation region due to the wavelength shift for example due to the Raman- scattering.

Additionally, the invention provides an apparatus according to one of the above described embodiments, wherein a waveguide comprises a phase shifter. By submitting the light in the waveguides to phase shifting relative to each other, the interference pattern is shifted. If the phase shifting is done in the waveguides of the focusing apparatus, the focus point of the focusing apparatus is moved, for example to scan at least part of the surface of the object to be examined. In its most simple configuration, the apparatus comprises only two waveguides. In this configuration, only a single phase shifter suffices as the phases of the light in the waveguides need to be shifted relative to each other. A preferred embodiment however, comprises a much larger number of waveguides. In such an embodiment all waveguides except one require a phase shifter in order to cause a phase shift between each waveguide. The waveguide that does not require a waveguide may optionally comprise a phase shifter too.

Likewise, phase shifters in the waveguides of the scattered light collector will result in the focus point of the first free propagation region to be moved, to, again, scan the surface of the object to be examined by collecting scattered light from different points of the object. This has the advantage that the focus point can be shifted, without moving the light focusing apparatus. This enables the scanning of a region on or in the objects to be examined by the focus point in order (in combination with a light detector) to scan at least parts of the object.

Alternatively, the phase shifters can also be used to scan through a range of wavelengths in order to determine the wavelength of the Raman-signal.

In a further embodiment a light focusing apparatus is provided, wherein the phase shifter comprises a heating element that is in thermal contact with the wave guide in order to heat the wave guide. Heating at least a part of the waveguide causes a change in the optical path length and therewith a phase change at the output end of the waveguide.

Alternatively, the invention provides a light focusing apparatus, wherein the waveguide comprises means to change the length of the optical path in the waveguide. Changing the length of the optical path of the waveguide relatively to another waveguide also causes the light exiting the waveguide in the free propagation region to be subjected to a phase shift with respect to the other waveguide. In this way a change in the interference pattern and focus point can be realized.

In a further advantageous embodiment an apparatus is provided wherein the apparatus is implemented in a SiP or a SoC. In again a further advantageous embodiment an apparatus is provided wherein the apparatus is implemented in semiconductor substrate. By implementing all elements of the apparatus in a SiP or a SoC a quite compact apparatus is obtained, as already described above, that can furthermore be produced cheaply in mass production.

In a specific embodiment an endoscope is provided comprising an apparatus according to one of the forgoing embodiments .

In an alternative embodiment the invention provides a data storage apparatus for the writing and reading of optically stored data, comprising an apparatus according to one of the above embodiments .

According to one aspect of the invention a method is provided for controlling the focus of a focused light source, comprising the steps of: providing a plurality of waveguides, with first ends for coupling light into the waveguides, and second ends forming an output grating line at a free propagation region, coupling light into the first ends of waveguides, and shifting the phase of the light in the waveguides, such that a converging wave front is generated in the free propagation region, and a focus point results in a desired position.

According to another aspect a method is provided for measuring the light scattered by or originating from a point of an object, comprising the steps of: providing a plurality of waveguides, wherein the first ends of the waveguides form an input grating line at a first free propagation region, and the second ends of the waveguides form an output grating line at a second free propagation region, placing the input grating line, such that a first focus point of the input grating line substantially coincides with a point of the object, lighting the point with a light source, and detecting the scattered light in a second focus point of the output grating line.

According to again another aspect a method is provided, further comprising the step of changing the phase shift of the waveguides in respect to each other, in order to change the position of the first and/or second focus point .

In again another aspect of the invention a method is provided for measuring the light scattering by an object, comprising the steps of the method for measuring the light scattered by a point of an object, wherein the step of lighting a point with light source, comprises the steps of the method for controlling the focus of a focused light source . Further advantages and embodiment will be discussed with reference to the appended figures, wherein:

Figure 1 shows a Raman-probe, according to the state of the art.

Figure 2 shows an embodiment of a light scattering detector, according to the present invention.

One particular advantageous embodiment according to the invention is a scattered light measuring device that is manufactured as a SiP or a SoC and comprises (figure 2) a light source comprising laser diode 202 for generating monochromatic coherent light. The light generated by the laser diode 202 is guided through an optical channel 232 to a free propagation region 222. The first ends of a number of waveguides 234a-c (only three waveguides are depicted, however, in practice, many more waveguides are implemented) form an input grating line in the free propagation region

222. The second ends of the waveguides 234a-c form an output grating line in another free propagation region 221. The light exiting the waveguides 234a-c generated an interference pattern, wherein the absolute maximum acts as a focus point in some biological tissue 210 that is to be examined.

The light in the focus point interacts with particles of the tissue or other material 210, causing light to be scattered. Scattered light is collected in the free propagation region 223. Connected to the free propagation region 223 is a number of waveguides 236a-c (Again, only three waveguides are depicted. In practice, many more waveguides are implemented) , the first ends thereof forming an input grating line in the free propagation region 223. The collected light then exits the waveguides 236a-c through the second ends of the waveguides 236a-c, that form an output grating line in a further free propagation region 224. The output grating line causes the light exiting the waveguides 236a-c to interfere. The global maximum of this interference pattern acts as a focus point. The light in the focus point is collected by an optical channel that guides the light to a light detector, in this case a photo diode 204.

The waveguides 234a-c are provided with phase shifters 244a-c in order to change the phase of the light in the waveguides 234a-c. A phase controller 252 is connected (264a-c) to the phase shifters 244a-c. By changing the relative phase between the phase shifters 244a-c, the position of the focus point of the light entering the tissue 210 can be controlled. The waveguides 236a-c of the scattered light collector are likewise provided with phase shifters 246a-c that are connected (266a-c) to the phase controller 252 in order to adjust the focus point of the free propagation region 223 in a synchronized manner to the focus point of the free propagation region 221 of the light focusing device. The scattered light measuring device further comprises a wavelength control device 254 for controlling the wavelength of the light source 202. The light source 202 might for example comprise an array of laser diodes that generate light of different wavelengths.

For the man skilled in the art it is clear that the embodiments mentioned above only comprise exemplary embodiments. The men skilled in the art will appreciate that many variations and adaptations of the exemplary embodiments are possible without departing from the invention. It is, for example, possible to combine the features of several embodiments to form further embodiments. It is further clear to men skilled in the art that the present invention is suitable for multiple applications. In addition to the applications already shown, one can for example think of, Raman- spectroscopy, diffusion- refleet ion- infrared spectroscopy (DRIFT) , luminescence spectroscopy and other types of optical spectroscopy, and confocal microscopy. The protection sought is therefore determined by the following claims.